1. Field of the Invention
The present invention concerns a fire protected steel structure and removable panels for fire protection of steel structures. The panels are intended for covering steel structures such as tubular elements, girders, tanks, flanges, valves, columns, panels, walls etc. in particular for offshore installations, process plants, vessels, or anywhere metal structures are used in an environment where fire protection is an issue.
2. Description of the Related Art
In fires in or close to steel structures, it is of considerable importance that the structures are sufficiently fire protected to maintain the functionality and ability to carry load. The steel structures may be of any shape, for instance cylindrical, square, shaped as girders, columns or walls.
Fires that occur in for instance hydrocarbon producing or processing installations may threaten the structural integrity of the carrying steel structures (girders/columns) of the installation. Failure of a load carrying steel structure of an installation may lead to considerable damage both to personnel and equipment and may result in considerable pollution.
Accordingly, it has been proposed to provide such installations with some sort of passive heat insulation, seeking to reduce the thermal loads on the structure in the event of a fire. When such fire insulation is tested, resistance against jets and hydrocarbon fires, fire and explosion loads should also be documented.
There are various requirements and standards for passive fire and explosion protection of steel structures throughout the world. In most cases a load carrying steel structure should be able to resist both jet and hydrocarbon fires from 60 to 120 minutes without the radiated temperature exceeding 400° C. The steel structures should in most cases also be able to withstand an explosion pressure of up to 0.3 bar. A flame temperature during jet or hydrocarbon fires may exceed way beyond 1300° C.
Examples of such standards include Norsok Standard S-001 N and R-004, UL Standard Fire resistance Rating ANSI UL 263 and ANSI/UL 1709. The solution of the present invention fulfils these standards.
Current passive fire protecting solutions for load carrying steel structures usually include expandable/intumescent, fire insolating epoxy substances or cement based light weight concrete. These substances are sprayed directly onto the structure to be protected.
This solution has some obvious disadvantages. Chisel and chisel hammer must normally be used to remove the fire protecting substance from the structure. Tools (for instance angle grinder) that heat the fire insolating substance should not be used as toxic hydrocyanic acid gasses may develop. Inspection of welding zones, corrosion damage, corrosion protecting coatings or any repair work or modifications is difficult when the protected structure is coated directly onto the surface.
Fire insolating epoxy substances are very difficult to apply in places with high humidity. Cement based light concrete is primarily used in these conditions. Light concrete that can be sprayed is however not impervious and absorbs humidity that contributes to corrosion. Furthermore, concrete has a tendency to deteriorate in time whereby the fire protecting properties are reduced.
A problem when using epoxy based substances is that high temperatures are required during application, and that the equipment used is not suitable for use in oil and gas installations due to the fire and explosion hazards. Substantially all the passive fire protection on oil and gas installations is applied manually. There are also considerable problems with fire insolating epoxy substances in terms of HSE. Hazardous gasses are released during application and in the period when the epoxy sets. This typically leads to epoxy allergy with the personnel, thus preventing any further work with epoxy.
It is a purpose of the present invention to provide a solution that fulfils the required standards, that not promotes corrosion, that not absorbs humidity, that has a reasonable weight, that allows integrity of the structure to be protected, that is easy to produce, that can be adapted to be used on a multitude of structures and that can be used under all relevant climatic conditions. Furthermore, it is an object to provide a solution with a life span of 25 years without substantial maintenance. It is also a purpose of the present invention to provide a system that can be installed without having to shut down the structure to be protected (eg. an offshore platform) for application. Furthermore it is a purpose to provide a system that can be installed in spite of an environment with explosion hazard. The solution should also satisfy all relevant requirements for HSE within the relevant sectors such as within the oil and gas industry.
An important feature with the invention is that instead of applying the passive fire protection directly onto the structure to be protected, prefabricated fire protecting panels are installed onto the structure to be protected while maintaining suitable conditions relating to ventilation, temperature and humidity. The solution of the present invention includes panels that are easy to remove to ease inspection of for instance welding zones, to check for corrosion, cracks, deformation and corrosion protecting coatings. The removable panels may also be adapted for a multitude of uses and as they are easy to remove, attachment of various equipment, repair operations and modifications is facilitated. The panels can be installed in environments exposed to fire and explosion hazards without requiring explosion protected equipment.
The epoxy layer used in the panels according to the invention will typically begin to expand when exposed to temperatures of more than 200° C. The layer typically expands to five times the initial thickness when it is exposed to jet and hydrocarbon fires. It is this expanded epoxy layer that provides the thermal insulation during fire. It should always be a distance between the protecting panels and the structure to be protected for allowing this expansion. The necessary distance will clearly depend on the thickness of the expanding layer. The fire protecting requirements, the thickness of the material to be protected and the time the material to be protected must maintain its integrity are decisive factors for determining the thickness of the epoxy layer.
The panels have very low thermal insulating properties before they are exposed to heat, and this is favorable as ideally the panels have the same temperature on the inside and the outside to prevent condensation on the structure to prevent corrosion.
The panel joints should generally be open, but will be sealed when the panels begin to expand at higher temperatures.
The panels may for instance be designed to withstand jet fires (gas fire) of 350 k/Wm2 of heat flux, suggesting temperatures considerably exceeding 1300° C. The panels have been tested for hydrocarbon fires with radiation heat of 1100° C.